This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A232113 #12 Aug 17 2018 11:01:50 %S A232113 1,2,3,2,5,4,5,4,5,4,5,4,5,4,3,4,3,2,3,2,1,2,1,2,3,2,3,4,3,4,5,6,5,6, %T A232113 7,8,7,8,9,10,11,8,11,12,13,12,9,10,13,16,15,12,9,12,15,16,15,12,9,12, %U A232113 15,14,13,12,11,12,13,12,11,10,9,10,11,10,9,8,7,8,9 %N A232113 a(n) is the Manhattan distance between n and 2*n in a square spiral of positive integers with 1 at the center. %C A232113 Spiral begins: %C A232113 . %C A232113 49 26--27--28--29--30--31 %C A232113 | | | %C A232113 48 25 10--11--12--13 32 %C A232113 | | | | | %C A232113 47 24 9 2---3 14 33 %C A232113 | | | | | | | %C A232113 46 23 8 1 4 15 34 %C A232113 | | | | | | %C A232113 45 22 7---6---5 16 35 %C A232113 | | | | %C A232113 44 21--20--19--18--17 36 %C A232113 | | %C A232113 43--42--41--40--39--38--37 %C A232113 . %C A232113 Numbers n such that a(n)^2=n: 1, 4, 16, 625, 20736, 707281, 24010000, 815730721, ...; that is, 1, 4, 2^4, 5^4, 12^4, 29^4, 70^4, 169^4, ... (cf. Pell numbers: A000129). %Y A232113 Cf. A000129, A214526, A232114, A232115. %K A232113 nonn %O A232113 1,2 %A A232113 _Alex Ratushnyak_, Nov 19 2013